The copolymer composition comprising a long chain C6-C12 polyfluoroalkyl group (hereinafter referred to as “Rf group”) has been utilized previously as the water- and oil-resistant agent for paper. On the other hand, US EPA (United State Environment Protection Agency) pointed out that the long chain Rf group produces perfluoro-octanoic acid (hereinafter referred to as “PFOA”) which might cause an influence on the environment. Therefore, many efforts have been made to develop a water- and oil-resistant agent for paper by using a fluorine-containing copolymer having a short chain Rf group. The water resistance and the oil resistance, however, tend to decrease along with the decrease of the carbon number of the Rf group, and the water- and oil-resistance is not satisfactory. So, further improvements have to be made to provide a paper having an enough water- and oil-resistance.
For example, Maekawa et. al. proposed a water- and oil-resistant composition comprising a fluorine-containing copolymer which comprises a fluorine-containing (meth)acrylate monomer having preferably a C1 to C6 Rf group, a cationic nitrogen-containing monomer such as diethylaminoethyl methacrylate, and polyoxyethyleneglycol mono(meth)acrylate (WO2005/090423A1). This water- and oil-resistant composition has the problem that bubbles of the aqueous solution are easily caused because of containing polyoxyethyleneglycol mono(meth)acrylate having high hydrophilicity, although water- and oil-resistance of the paper is improved.